Most of the IT farm's job interview or written exam has at least one question regarding OSI or TCP/IP model. Some questions of this topic are presented here with very concise answers. All these questions are very helpful for the interviewee. Posts like "IT Executive", "Network Engineer", "Junior System Engineer" etc. have such type of questions in the job selection written exam. These questions will also helpful for strengthening basic knowledge of OSI model also.

• Question and Answers are arranged sequentially.
• "BOLD Font" indicates Question.
• "Normal Font" indicates Answer.

"Segment" is a PDU (Protocol Data Unit) of Transport layer of OSI model.

PDU for Network Layer is: "Packet" and PDU for Data Link Layer is :"Frame"

Network layer.

By using "Telnet"

DNS uses both TCP or UDP or both. UDP can handle only 512bytes. If data size is withing 512 bytes UDP is used, otherwise, TCP is used.

Which layer is closer to the user?

Upper layer i.e. Application layer is closer to the user.

Differentiate between forward lookup and reverse lookup in DNS?

• Forward lookup is: name-to-address,
• Reverse lookup is: address-to-name.

what are the difference between TCP and UDP?

• TCP: Connection oriented protocol, acknowledged one, Point to point communication.
• UDP: Connection less protocol, unreliable, less traffic

What is IPSec?

IPSec is "Internet Protocol Security". It is a suite of protocols for securing Internet Protocol(IP) communications.

What is the way to establish a TCP connection?

By using acknowledgement.

What is the difference between flow control and error control?

• Flow control: adjust and confirm data flow rate for successful transmission.
• Error Control: a way to recover corrupted data .

Mark one of the most important difference between TCP and UDP.

TCP is a connection-oriented and UDP is a connection-less protocol

Mention one real place to use TCP/IP.

LAN cards

What is the responsibilities of Network Layer?

• Logical addressing
• Best effort delivery

Data link layer is sub-divide into how many groups?

• 2 sub-divided groups: MAC Layer and LLC layer
• MAC: Media Access Control/Medium Access Control
• LLC: Logical Link Control

What is the port number of Telnet and DNS?

Telnet = 23 and DNS = 53

What is the port number of ftp(data) and ftp?

ftp(data) = 20 and ftp=21

ARP resolves what? Address or IP?

ARP stands for Address Resolution Protocol. It helps to find the hardware address or MAC address when IP address is known.

Which layer of OSI is responsible for end-to-end communication?

Transport layer.

Why we have to use router?

To communicate several networks, routers are used. Routers have both broadcast domain and collision domain.

RARP resolves what? Address or IP?

RARP stands for Reverse Address Resolution Protocol. It helps to find the IP address when physical or hardware or MAC address is known.

What is OSI model?

OSI model is a reference model containing 7 layers such as physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.

What is TCP/IP model?

TCP/IP model is an implementation of OSI reference model. It has five layers. They are: Network layer, Internet layer, Transport layer and Application layer.

What is the full form of OSI and TCP/IP model?

• OSI stands for = Open Systems Interconnection (OSI) model
• TCP/IP stands for = Transmission Control Protocol/ Internet Protocol

What are the differences between OSI and TCP/IP model?

Important differences are:

OSI is a reference model and TCP/IP is an implementation of OSI model.

OSI has 7 layers whereas TCP/IP has only 4 layers The upper 3 layers of the OSI model is combined on the TCP/IP model.

OSI has: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer TCP/IP has : Network layer, Internet layer, transport layer and application layer.

What are the differences among router, switch, bridge and hub?

All of them are devices and are used in network. Their differences are:

• Router: Layer 3 device, can work on physical, data and network layer.
• Switch: Layer 2 device, can work on data link layer
• Bridge: Layer 2 device, can work on data link layer.
• Hub: Layer 1device, just a multi-port repeater and works on physical layer

Switch operates on which layer of OSI model?

Normal switch operates at Layer 2 i.e. data link layer and Intelligent switch operates at Layer 3 i.e. network layer.

What is the upper layer name of OSI layer?

Application layer.

Name 4 example of application layer?

DNS, FTP, Telnet, http

How does ARP response the request?

ARP sents the request in broadcast, response is unicast

Error control is down in which layer?

Layer 4

Name the 2 sublayers of data link layer.

MAC sublayer and LLC sublayer

How is data send by IP layer?

IP layer PDU is "packet". So, data is send as packet.

TCP/IP has how many layers?

5 layers: Network layer, Internet layer, Transport layer and Application layer.

What is the data unit of "Transport layer"?

Segment

What are the differences of MAC sublayer and LLC sublayer?

In fact, Data Link layer has 2 sublayes: MAC sublayer & LLC sublayer.

• MAC sublayer(802.3): defines how to transmit data on physical layer
• LLC sublayer(802.2): responsible for identifying different protocol logically & encapsulate them.

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